Merge #15153: gui: Add Open Wallet menu

1951ea434 gui: Show indeterminate progress dialog while opening walllet (João Barbosa)
8847cdaaa gui: Add OpenWalletActivity (João Barbosa)
4c8982a88 interfaces: Avoid interface instance if wallet is null (João Barbosa)
be82dea23 gui: Add thread to run background activity in WalletController (João Barbosa)
6c49a55b4 gui: Add Open Wallet menu (João Barbosa)
32a8c6abf gui: Add openWallet and getWalletsAvailableToOpen to WalletController (João Barbosa)
ab288b4e5 interfaces: Add loadWallet to Node (João Barbosa)
17abc0fd5 wallet: Factor out LoadWallet (João Barbosa)

Pull request description:

  The *Open Wallet* menu has all the available wallets currently not loaded. The list of the available wallets comes from `listWalletDir`.

  In the future the menu can be replaced by a custom dialog.

  <img width="674" alt="screenshot 2019-01-12 at 12 17 02" src="https://user-images.githubusercontent.com/3534524/51073166-ac041480-1664-11e9-8302-be81702bc146.png">

Tree-SHA512: ebfd75eee0c8264863748899843afab67dadb7dff21313c11e3cb5b6108d954978dd1f1ae786bc07580c5a771ea4ab38d18c1643c9b9b3683ed53f0f6c582e38

src/interfaces/node.cpp

@@ -42,6 +42,7 @@ class CWallet;
 fs::path GetWalletDir();
 std::vector<fs::path> ListWalletDir();
 std::vector<std::shared_ptr<CWallet>> GetWallets();
+std::shared_ptr<CWallet> LoadWallet(interfaces::Chain& chain, const std::string& name, std::string& error, std::string& warning);
 
 namespace interfaces {
 
@@ -252,6 +253,10 @@ public:
         }
         return wallets;
     }
+    std::unique_ptr<Wallet> loadWallet(const std::string& name, std::string& error, std::string& warning) override
+    {
+        return MakeWallet(LoadWallet(*m_interfaces.chain, name, error, warning));
+    }
     std::unique_ptr<Handler> handleInitMessage(InitMessageFn fn) override
     {
         return MakeHandler(::uiInterface.InitMessage_connect(fn));